This invention is an improvement of the so called "manure spreader" which is an apparatus for hauling animal wastes to a suitable location where they can be unloaded or spread in a uniform manner over an area of ground to gain the fertilizer value contained in the waste. Typically they are wheeled vehicles having a load box or bed, which can be pulled by a tractor or other vehicle to a designated spreading area. An unloading mechanism can be actuated which provides a continuous delivery of the load in the load box toward the rear end of the spreader. The rear end of the spreader generally contains a broadcasting device or thrower which will spread the load as delivered uniformly over a fairly sizeable area as the spreader moves along.
Conventional spreaders contain a series of spaced parallel bars transverse to the direction of travel, lying on the floor of the load box which are separated from each other. The ends of the bars are fixed to chains positioned near the sides of the floor of the load bed which rest on the load bed floor. The chains each form a loop running above and below the load bed floor. Each chain turns about idlers or sprockets located at front and rear of the spreader wherein the loop is disposed in a vertical plane running longitudinally in the direction of travel. The chains are powered to drag the bars or slats slowly across the floor of the load bed towards the rear of the spreader. This action drags the load of waste gradually towards the rear most end of the spreader so that a supply of waste is fed to the thrower at the rear of the machine until the load is distributed. The distribution usually occurs while the vehicle is in motion so that a uniform pattern of distribution over an area is obtained.
Operation of this type of unloader is obtained by engaging or disengaging the power that drives the chains which in turn moves the slats across the load bed floor. This action continues until the load is emptied. Difficulties with this type of unloader are encountered when "bridging" of the load occurs or when the slats freeze to the load or floor in very cold weather and thus prevent operation or cause damage or breakage of the chains or drive system. Bridging occurs when the load does not fall down onto the area where the moving bars are located and when the underneath material is pulled out by the moving bars a tunnel remains which will not by itself unload further. The operator does not have positive control of the unloading with the conventional spreader and slow and uneven spreading tends to occur at the end of each unloading cycle. Additional time is required to attempt to clean out the load bed with the moving bars and chains and manual clean-up is sometimes required. A condition called "fallback" tends to occur toward the end of the unloading cycle with certain manure or manure-straw combinations whereby the material tends to roll away from the thrower by falling back towards the front of the machine which adds time to the process and reduces the uniformity of spreading.
Another type of manure spreading device in use contains the same features as indicated above except that the unloading mechanism consists of an upright wall transverse to the main axis of the spreader. The wall is powered by one or more hydraulic cylinders and can be retracted into the area near the front of the spreader. The wall rests on the load bed floor and can slide along it. Once the spreader is loaded and ready for discharge, the hydraulic control system provides power to the hydraulic cylinders in a controlled manner so that the cylinders slowly push the upright wall along and consequently the load moves along the floor towards the rear of the spreader where the rotating distributor is located.
The cylinders or a control system for the cylinders is designed to stop the upright wall at the rear of the machine before it reaches the moving parts of the distributor. Usually this is obtained by limiting the design length of the hydraulic cylinder or cylinders. The power comes from the hydraulic system of the tractor itself and through a valve and hoses or tubes is connected to the hydraulic cylinders of the spreader so that reversing the direction of the hydraulic flow to the cylinders will cause the cylinders to retract to the beginning position to complete the cycle.
This device has the difficulties of high cost particularly for design and construction of hydraulic cylinders sufficiently large to provide motion of the wall through the entire length of the load bed. It has the additional difficulty that in cold weather a partially frozen load can cause damage to the mechanical components if full working pressure of the hydraulic system is applied and it may fail to unload if a substantially lower pressure is applied through an internal relief valve. Devices of this kind are subject to non-uniform and varying resistance from the load and for certain consistencies of material can result in "compression" of the load causing it to have different characteristics at different points in the unloading cycle or causing it to rise up so that varying volumes of material are presented to the thrower at different times.